Issue 2, 2018
Sea Turtle Conservancy (STC) has been working in the Bocas del Toro region (which incorporates the Province of Bocas del Toro and the indigenous Ngäbe-Bugle Comarca) since 2003. Several leatherback nesting beaches have been monitored in the Bocas region since the 1990s under the auspices of a variety of government and non-government organizations. While STC’s monitoring program originally focused on hawksbill sea turtles, the 24 km Chiriquí Beach was identified as the most important leatherback nesting beach in the region, if not the wider Caribbean, where 1,000 – 7,000 nests are recorded each season. In addition to Chiriquí Beach, there are other beaches in the Bocas region with leatherback nesting, including Soropta Beach hosting 500 – 1,000 nests per season; Bluff Beach with 100 – 300 nests per season; and Long Beach with 100 – 300 nests per season.
Leatherback nesting in the Bocas region begins in mid-February and runs through mid-July, with peak nesting occurring in May. Unlike hawksbill turtles, leatherbacks and their eggs are not consumed by the local Ngäbe residents of the communities adjacent to the nesting beach within the Comarca community. However, on beaches outside of the Comarca, in the northern part of the Bocas region, leatherback eggs are actively collected and even some females are killed for their eggs. In 1999, approximately 30 leatherbacks were found killed by turtle hunters during a ground survey of Soropta Beach. Since 2003, the mortality of nesting females has decreased by 90%, in part because of the presence of STC’s research and monitoring programs.
Based on STC’s flipper tagging efforts, STC has documented that leatherback turtles in the Bocas region have highly variable nesting beach selection and do not follow the traditional theory that sea turtles always return to the specific beach where they hatched. Between nesting seasons, and even during the same nesting season, female leatherbacks flipper tagged while nesting in the Bocas region were also encountered nesting on beaches in Costa Rica (Gandoca, Pacuare and Tortuguero), Colombia (Playona), and outside of the Bocas region in Panama (Sixaola, San San, Armila and Punta Rincon). The nesting distribution and abundance data from STC’s leatherback nesting beach monitoring program support the idea that the Bocas region leatherbacks are part of a southwest Caribbean metapopulation. This metapopulation includes nesting populations from Costa Rica, Panama and Colombia, with Chiriquí Beach being the most important beach.
In addition to monitoring the nesting beaches in the Bocas region, STC has been tagging nesting leatherbacks with satellite transmitters since 2003 to track their movements after they depart the nesting beach. Leatherbacks are wide ranging, long-distance migrating marine turtles that have been characterized as wandering foragers. This is in contrast to other species of sea turtles that tend to migrate from nesting beaches to specific foraging areas and remain in those foraging areas until ready to return to their nesting beach after 2 to 3, or more, years. Between 2003 and 2017, a total of 32 leatherbacks from the southwest Caribbean metapopulation were satellite tagged after nesting in Costa Rica or Panama. STC researchers used a movement model to separate migration vs. foraging behavior and locations. This inforamtion was then used to identify leatherback foraging areas and try to characterize the environmental conditions of these areas.
Based on the recovery of leatherback flipper tags, STC expected the vast majority, if not all of the satellite tagged leatherbacks to migrate to foraging areas in the North Atlantic Ocean (see map above). But, satellite tracking revealed that more than half of the leatherbacks migrated into the Gulf of Mexico for foraging, while the rest migrated into the North Atlantic Ocean. Once in the Gulf of Mexico, leatherbacks did not leave the Gulf for the duration of their tracking. Gulf of Mexico turtles swam an average of 8,187.05 km over 202 days, while leatherbacks in the North Atlantic swam an average of 13,481.02 km over 298 days.
Using a GIS program, STC was able to identify two important foraging areas within the Gulf of Mexico and one along the eastern coast of the United States. It also appears that peaks in leatherback occurrence in a foraging area often followed peaks in ocean Chlorophyll-a or organic carbon concentrations. These are both indicators of ocean productivity and possible areas for leatherbacks to find food. In addition to the importance of the Gulf of Mexico to the southwest Caribbean metapopulation of leatherbacks, the movement model suggests that leatherbacks in the Gulf of Mexico have a different foraging strategy than leatherbacks feeding in the North Atlantic Ocean.
STC’s research and conservation efforts along the Caribbean coast of Costa Rica and Panama are leading the way in new discoveries of behavior for leatherbacks from the southwest Caribbean metapopulation. The use of multiple nesting beaches by the same turtle and different feeding strategies based on where leatherbacks migrate are important considerations when developing conservation and management strategies for these endangered turtles.
Sea Turtle Conservancy
